Jan. 19, 2014 — During the abrupt cooling at the onset of the so-called Younger Dryas period 12680 years ago changes in the water cycle were the main drivers of widespread environmental change in western Europe. Thus, the regional impacts of future climate changes can be largely driven by hydrological changes, not only in the monsoonal areas of the world, but also in temperate areas.

The role of the hydrological cycle during abrupt temperature changes is of prime importance for the actual impact of climate change on the continents. In a new study published in Nature Geoscience online (January 19, 2014) scientists from the University of Potsdam, Germany and the GFZ German Research Centre for Geosciences show that during the abrupt cooling at the onset of the so-called Younger Dryas period 12680 years ago changes in the water cycle were the main drivers of widespread environmental change in western Europe. The team of scientists analyzed organic remains extracted from Meerfelder maar lake sediments from the Eifel region, western Germany, to reconstruct changes in precipitation patterns in unprecedented detail. They were able to show that the intrusion of dry polar air into western Europe lead to the collapse of local ecosystems and resulted in the observed widespread environmental changes at that time.

The exact sequence of events during abrupt climate changes occurring over only a few years is one of the great unknowns in paleoclimate research. The new results presented here were obtained by using a novel method, where molecular organic remains derived from plant fossils were extracted from precisely dated annually laminated lake sediments. The ratio of the heavy Deuterium to the light Hydrogen isotopes in these biomarkers can be used to reconstruct changes in precipitation regime and moisture sources with unprecedented detail.

The Younger Dryas period was the last major cold period at the end of the last glaciation with a duration of about 1100 years, when an abrupt change in the pathway of westerly wind systems [jet stream dips] over Europe lead to massive environmental change within a few years, as GFZ scientists showed in an earlier study. Dirk Sachse, the head of the workgroup at the Institute of Earth and Environmental Sciences of the Potsdam University explains: "In our new study we can show for the first time that this change in the pathway of westerly wind systems brought dry polar air into western Europe and this was the ultimate cause for the widespread disappearance of forests in the area."

With these new results, the group also supports the hypothesis that this change in atmospheric circulation patterns over western Europe took place 170 years after the onset of cooling, as observed in the Greenland Icecores. The authors attribute this delay to the subsequent southward expansion of sea ice in the North Atlantic following the onset of cooling. This lead to a southward shift of the polar front channeling dry polar air into western Europe. "Our results also show that abrupt climate and environmental change may not be coeval on large regional scales, but can take place with substantial regional and temporal delays" explains Prof. Achim Brauer from the GFZ German Research Centre for the Geosciences.

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I thought there were several theories related to climate change and near extinctions 13,000 years ago. In Guns, Germs, & Steel, Jared Diamond postulates that early humans hunted big animals to extinction when they moved to N. America as the animals were not afraid of humans. I also remember the Clovis people kind of disappeared at this time and one theory was that a meteor shower set most of N. America on fire and killed many species and set back humans for thousands of years. There is a layer of black ash all over N. America at this time. So perhaps the smoke from all the fires cooled the globe which then affected the water cycle and diverted the polar vortex. All very interesting. And NOT settled science.